1. Field of the Invention
This invention relates to nuclear reactors, and more particularly to reactor internals apparatus for baffling reactor coolant flow into and about the reactor core.
2. Description of the Prior Art
A typical nuclear reactor core includes a plurality of fuel assemblies positioned adjacent one another so as to approach the configuration of a right circular cylinder. The core typically seats upon and is supported by a lower core plate which in turn is supported by a flow control and support structure, such as a core barrel surrounding the core radial periphery. As the core barrel must support this large load, it is a relatively thick-walled massive structure. The core barrel, however, must be spaced from the peripheral core assemblies to alleviate the effects of irradiation upon the barrel wall. Also, cool reactor coolant entering the vessel passes about the outer surface of the core while the coolant passing through the core is hotter. Therefore, spacing the barrel from the core also protects the barrel wall from an excessive thermal gradient. It is, however, undesirable to allow a large flow of coolant to bypass the core in the area between the barrel and core, as the bypass flow detracts from the reactor thermal efficiency.
A baffle plates and formers assembly has therefore been utilized to baffle flow into and immediately about the core, while also providing an acceptable bypass coolant flow. This assembly has included a plurality of longitudinally positioned baffle plates each extending throughout the core height, and abutting against one another about the core periphery. The baffle plates are affixed to and supported by transversely positioned formers, which are supported by the core barrel. The barrel, baffle plates, and formers are affixed by fasteners, such as welds or, more typically, bolts. Because the barrel is relatively thick walled, and the baffle is relatively thin walled, they experience a thermal expansion differential that must be accommodated by the fastening means affixing the barrel, baffle plates, and formers, such as the bolts. With increased reactor core lengths, the differential expansion and resulting loads are increased even more. The resulting loads on the fasteners are significant, and can potentially result in failure. Also, the differential expansion can cause bending of the baffle plates, resulting in potential interference with the fuel assemblies and undesirable changes in the coolant flow. Particularly, enlarged gaps may occur between adjacent baffle plates, allowing cross flows which detrimentally vibrate the fuel assemblies.
It is therefore desirable to provide a baffle arrangement which not only baffles coolant flow into and about the core and provides cooling of the baffle and support components, but which also alleviates the large stresses and loads imposed upon the components and the fasteners affixing these components.